Cylinder 4 misfire on start?

[JJMaine]

The other morning I started my truck and it shuttered for a few seconds before starting. It threw a CEL and it was a cylinder 4 misfire. I cleared the code and since then it has started and run fine.

I've had the truck for about 10k miles (it has 113,000 miles on it now) and put new plugs on it when I bought it. The funny thing is, when I changed the plugs, cylinder number 4 had a different brand sparkplug in it which I thought was strange at the time but now it makes sense lol. I had noticed the truck started a little rough from time to time but nothing too crazy.

Like I said, I put new Motorcraft plugs in 10k miles ago. Would it be worth it for less than $100 to put on a new OEM coil and plug wires? Should I change the plugs again already or just the coil and wires? Thanks!

 

[JJMaine]

I found the picture from when I changed my plugs. The far left came from cylinder 4 (I just numbered them in the order that I took them out). It is an AutoLight where the rest were Motorcraft.

Cylinder 4 is drivers side all the way towards the front of the truck right?

 

[SenorNoob]

Is 4 longer or just the angle of the shot?

The first one definitely doesn't have as much carbon build up. Likely not firing unless it was changed later. Considering it's a different brand, quite possible.

 

[JJMaine]

Not sure as I tossed em last summer. In the for sale ad, the previous owner said he had just had plugs and wires done but I highly doubt that. Unless a shop told him they did. My guess is he had the same random cyl. 4 misfire and just replaced that plug to try and cure it.

If you look in my previous posts/threads I've been trying to figure out a bit of a rough idle but just learned to live with it. Maybe it's all connected? I ordered a new OEM coil and wires from Rock Auto and hopefully that does the trick. If not, my truck has 115k miles so I'll consider it preventative maintenance anyway lol.

 

[JJMaine]

While I'm here, yesterday on the way home from work I was sitting at a stop light and I felt/heard the ac compressor kick on and the truck shuddered and lost rpm. Just that one time so far but I'm hoping the coil and wires might fix that too???

 

[JJMaine]

So I put new OEM coil and plug wires on this weekend. Truck started and seemed to run smoother (maybe just imaging it?). Then it sat all weekend as I was busy with home projects.

This morning it started a little odd though and didn't quickly idle up to 1500rpm before dropping down which I thought was weird. When I came out of the store near my work truck cranked and wouldn't start. It took me a few tries to get it started. Once running it's fine it seems (so far). What's my next step? Fuel pump maybe?

No CEL this time ...

 

[JJMaine]

Well, I'm still trying to figure this out. I thought I had fixed the issue with a new OEM fuel pump relay. Then this morning it started rough again and it threw 2 codes. P0300 (random/multiple misfires) and p0304 (cylinder 4 misfire). The truck has a new air filter, fuel filter, plugs, coil and wires all OEM parts. I'm done firing the parts cannon at this thing but it's hard to diagnose with any certainty since it happens so randomly. I would like to figure it out before it leaves me stranded somewhere lol

Could the IAC cause this? I took that off and cleaned it but it already looked pretty darn clean. Could still be malfunctioning?

My next guess would be a crappy fuel pump. I could buy a meter and test fuel pressure but here again, would it show low pressure every time or only once a month at random when I get misfire codes.

The fact that cylinder 4 always seems to be involved seems suspicious. I could get a compression tester as well but if that cylinder was low wouldn't I always get a misfire? I'm stumped and not a mechanic so if anyone has any ideas I'd be greatful, thanks guys!

Also only seems to be on start up, even when it starts shitty and throws a code, the truck still runs perfectly fine.

 

[mikkelstuff]

What engine?

I ask because my 2002 3.0L does the same - intermittent misfire on cylinder number 4.

A can of the expensive BG-44K fuel system cleaner will clear the misfire for a couple of tanks worth of gasoline.

I first had the cylinder number 4 injector replaced which fixed the problem but 10 years and 16,000 miles later, it has come back again.

Why only cylinder number 4? Once again a can of BG-44K cleared up the problem for a time. So I'm debating changing out the cylinder number 4 injector once again but I would like to understand why this is always and only cylinder number 4.

 

[JJMaine]

4.0 SOHC

 

[JJMaine]

Spent the afternoon going to HF and buying a fuel pressure tester.

Turns out I have no pressure-low pressure (it varies) when I turn the key on but 65psi with the truck running. I guess fuel pump?

If I keep turning the key to the off and then on again position the fuel pressure rises about 10psi each time.